Conjugated Polymer Nanoparticles: Preparation, Applications In Phototherapy, Anti-counterfeiting And White LED

Conjugated polymer nanoparticles exhibit exceptional fluorescence brightness, excellent stability and good biocompatibility, so they have been widely applied in chemistry, materials science and bioscience, and many other fields. Conjugated polymer nanoparticles have been demonstrated for a wide variety of biological imaging and biosensors due to their outstanding optical properties. In this thesis,valuable explorations have been carried out on the preparation of conjugated polymer nanoparticles with excellent properties and their applications in phototherapy, anti-counterfeiting and white LED. The results of this dissertation can be described as follows.1. Conjugated polymer nanoparticles have large absorption cross sections so that they can transfer efficiently energy to small molecule fluorophores by fluorescence resonance energy transfer. The nanoparticles comprised of conjugated polymer and photosensitizer are developed as novel photosensitizers. We synthesized a series of conjugated polymers with porphyrin units at different molar fractions and then systematically characterized the spectroscopic properties of these nanoparticles, which showed efficient singlet oxygen generation amplified by inter-particle energy transfer. The photosensitizer leaching experiment was performed to investigate the stability of these nanoparticles. PFBT-TPPx nanoparticles possess excellent stability that overcome the photosensitizer leaching problem. The effectiveness of PFBT-TPPx nanoparticles as photodynamic therapy（PDT）photosensitizer was demonstrated by in vitro assay, which indicated that these nanoparticles are able to damage cancer cells under low nanoparticles concentration and light dose. Moreover, in vivo photodynamic therapy by using these nanoparticles was further investigated with xenograft tumors in Balb/c nude mice, which showed that the tumors were significantly inhibited or eradicated in certain cases. These results indicate that covalently TPP-incorporated conjugated polymer nanoparticles could be used as a promising candidate for PDT treatment.2. In conventional PDT, cancerous cells are locally killed by reactive oxygen species（ROSs）. Hydroxyl radical（?OH） presents the highest reactivity among ROSs, We developed a glucose oxidase-conjugated polymer dots（Pdots-GOx） system to generate hydroxyl free radicals for highly efficient photodynamic therapy. In the presence of H2 O andO₂, glucose oxidase can selectively catalyze the conversion of D-glucose into gluconic acid, accompanied by the generation of H2O2. Furthermore, under blue light（460nm）irradiation, H2O2 is photolyzed to produce hydroxyl free radicals. The effective tumour uptake of nanoparticles indicated that the enhanced permeability and retention effect（EPR） of tumor can help to trap these nanoparticles in the tumor site. The effectiveness of Pdots-GOx as PDT photosensitizer was demonstrated by in vitro assay, which indicated that the system are able to damage cancer cells under low concentration and light dose. Moreover, In vivo photodynamic therapy by using the system was further investigated with xenograft tumors in Balb/c nude mice, which show that the tumors were significantly inhibited or eradicated in certain cases. The system represents promisiong nanomedicine for improved photodynamic therapy as well as fluorescence imaging and long-time tracking.3. Fluorescent anti-counterfeiting has been playing an important role in modern commercial society and daily life. A variety of fluorescent nanomaterials have been used as fluorescent anti-counterfeiting inks. However, they still face with biological toxicity, environmental pollution, and many other challenges. Tricolor fluorescent inks based on conjugated polymer nanoparticles were prepared for anti-counterfeiting. We demonstrate the inkjet printing method for creating flexible full color patterns. The resulting image patterns show extraordinary stability, as evidenced by various chemical and physical treatments, offering a superior combination of bright fluorescence, light fastness, chemical and laundry resistance. These results show that fluorescent patterning based on conjugated polymer nanoparticles is well suitable for light display and anti-counterfeiting printing.4. While conjugated polymer nanoparticles have exhibited excellent stability, they still face with many challenges in light display and light emitting. To overcome these problems, semiconductor conjugated polymer dots（Pdots） were encapsulated into SiO2 matrix to form fluorescent nanocomposites by a modified St?ber method. The results of TEM exhibited that the size of SiO2-encapsluted nanoparticles is about 300 nm. Photostability studies indicated that the photostability of SiO2/Pdot were significantly improved as compared to the pure semiconductor polymer nanoparticles. By combining the phosphors with a blue chip, we obtained the WLEDs with high color rendering index（Ra=90.2）.5. The fluorescence brightness and stability are important features of conjugated polymer nanoparticles in the applications of fluorescence imaging and light display. We explored to improve the fluorescence brightness and photostability of conjugated polymer nanoparticles by hydrothermal treatment. Firstly, we explored the conditions of hydrothermal treatment and the processing temperature in the range of 40-200℃. Moreover, the fluorescence intensity and the quantum efficiency of conjugated polymer nanoparticles were measured before and after treatment. According to the results obtained, we chose the optimum temperature of hydrothermal treatment. In addition, the size of conjugated polymer nanoparticles was nearly unchanged after or before treatment. Photostability studies were employed to further investigate the stability of conjugated polymer nanoparticles before and after treatment. Our results showed that hydrothermal treatment could apparently enhance the fluorescent brightness and the stability of these nanoparticles. The results provide new ideas and new methods for further optimizing the optical properties of the conjugated polymer nanoparticles.